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//TestInt.java public class TestInt{ int year ;//¥¤¥ó¥¹¥¿¥ó¥¹ÊÑ¿ô public static void main(String[] args){ TestInt test = new TestInt() ; test.echo() ; } void echo() { System.out.println("year = " + year) ; } } ¥ª¥Ö¥¸¥§¥¯¥È»²¾È¤Î¥¤¥ó¥¹¥¿¥ó¥¹ÊÑ¿ô¤ÎÎã
//TestObject.java public class TestObject{ String name ;//½é´ü²½¤·¤Æ¤¤¤Ê¤¤ String echo(){ return name ; } public static void main(String[] args){ TestObject test = new TestObject() ; System.out.println(test.echo()) ; } } ¤³¤Î¾ì¹ç¡¢¥¤¥ó¥¹¥¿¥ó¥¹ÊÑ¿ô¤Ï½é´ü²½¤µ¤ì¤Æ¤¤¤Ê¤¤¤Î¤Ç¡¢¡Önull¡×Ãͤò¤È¤ë¡£¡Önull¡×ÃͤΤâ¤Î¤ò¼Â¹Ô¤¹¤ë¤È¡¢¼Â¹Ô»þNullPointerException¤¬µ¯¤¤ë¡£Î㤨¤Ð¡¢null»²¾È¤Î¤â¤Î¤ËÂФ·¤Æ¡¢¥É¥Ã¥È±é»»»Ò¤òÍѤ¤¤Æ¥¢¥¯¥»¥¹¤·¤Æ¤ß¤ë¤ÈÎã³°¤¬È¯À¸¤¹¤ë¡£
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//TestObjectError.java public class TestObjectError{ String name ; String echo(){ return name ; } public static void main(String[] args){ TestObjectError test = new TestObjectError() ; String s = test.echo() ; System.out.println(s.toLowerCase()) ;//¡ } } ¡¤Î¥¤¥ó¥¹¥¿¥ó¥¹ÊÑ¿ô¤Ï¡Önull¡×ÃÍ¡£¤³¤ÎÃͤǥ᥽¥Ã¥ÉtoLowerCase()¤Ë¥¢¥¯¥»¥¹¤¹¤ë¤È¡¢¼Â¹Ô¥¨¥é¡¼¤¬µ¯¤¤ë¡£name»²¾ÈÊÑ¿ô¤Ï¤¬¥ª¥Ö¥¸¥§¥¯¥È¤ò»²¾È¤·¤Æ¤¤¤Ê¤¤¤«¤é¡£»²¾ÈÊÑ¿ô¤¬¡Önull¡×¤«¤É¤¦¤«Ä´¤Ù¤Æ¤«¤é¼Â¹Ô¤¹¤ë¤È¥¨¥é¡¼¤¬µ¯¤¤Ê¤¤¡£
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public class TestObjectErrorRevision{ String name ; String echo(){ return name ; } public static void main(String[] args){ TestObjectErrorRevision test = new TestObjectErrorRevision() ; String s = test.echo() ; if(s != null){ System.out.println(s.toLowerCase()) ; } } } ÇÛÎó¤Î½é´üÃÍ
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class TestSub{ } public class TestArrangement{ static int[] b = new int[3] ; public static void main(String[] args){ for(int k = 0 ; k < b.length ; k++){ System.out.println(b[k]) ; } int[] a = new int[5] ; for(int i = 0 ; i < a.length ; i++){ System.out.println(a[i]) ; } TestSub[] test = new TestSub[4] ; for(int j = 0 ; j < test.length ; j++){ System.out.println(test[j]) ; } } } ¥í¡¼¥«¥ëÊÑ¿ô
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public class TestLocalBase{ public static void main(String[] args){ int a ;//¥í¡¼¥«¥ëÊÑ¿ô System.out.println(a) ; } } ¥ª¥Ö¥¸¥§¥¯¥È·¿¥í¡¼¥«¥ëÊÑ¿ô¤ÎÎã
public class TestLocalInstance{ public static void main(String[] args){ TestLocalInstance test ; if(test == null){ System.out.println("null") ; } } } main¥á¥½¥Ã¥É¤ËÅϤµ¤ì¤ë¥³¥Þ¥ó¥É°ú¿ô
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public class TestMain{ public static void main(String[] args){ for(int i = 0 ; i < args.length ; i++) { System.out.println(args[i]) ; } } } |
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